Stents are generally known. Indeed, the term "stent" has been used interchangeably with terms such as "intraluminal vascular graft" and "expansible prosthesis". As used throughout this specification the term "stent" is intended to have a broad meaning and encompasses any expandable prosthetic device for implantation in a body passageway (e.g. a lumen or artery).
In the past six to eight years, the use of stents has attracted an increasing amount of attention due the potential of these devices to be used, in certain cases, as an alternative to surgery. Generally, a stent is used to obtain and maintain the patency of the body passageway while maintaining the integrity of the passageway. As used in this specification, the term "body passageway" is intended to have a broad meaning and encompasses any duct (e.g. natural or iatrogenic) within the human body and can include a member selected from the group comprising: blood vessels, respiratory ducts, gastrointestinal ducts and the like.
Initial stents were self-expanding, spring-like devices which were inserted in the body passageway in a contracted state. When released, the stent would automatically expand and increase to a final diameter dependent on the size of the stent and the elasticity of the body passageway. Such stents were known in the art as the Wallstent.TM..
The self-expanding stents were found by some investigators to be deficient since, when deployed, they could place undue, permanent stress on the walls of the body passageway. This led to the development of various stents which were controllably expandable at the target body passageway so that only sufficient force to maintain the patency of the body passageway was applied in expanding the stent.
Generally, in these later systems, a stent, in association with a balloon, is delivered to the target area of the body passageway by a catheter system. Once the stent has been properly located (the target area of the body passageway can be filled with a contrast medium to facilitate visualization during fluoroscopy), the balloon is expanded thereby expanding the stent so that the latter is urged in place against the body passageway. As indicated above, the amount of force applied is at least that necessary to maintain the patency of the body passageway. At this point, the balloon is deflated and withdrawn within the catheter, and subsequently removed. Ideally, the stent will remain in place and maintain the target area of the body passageway substantially free of blockage (or narrowing).
A stent which has gained some notoriety in the art is known as the Palmaz-Schatz.TM. Balloon Expandable Stent (hereinafter referred to as "the Palmaz-Schatz stent"). This stent is discussed in a number of patents including U.S. Pat. Nos. 4,733,665, 4,739,762, 5,102,417 and 5,316,023, the contents of each of which are hereby incorporated by reference.
Another stent which has gained some notoriety in the art is known as Gianturco-Roubin Flex-Stent.TM. (hereinafter referred to as "the Gianturco-Roubin stent"). This stent is discussed in a number of patents including U.S. Pat. Nos. 4,800,882, 4,907,336 and 5,041,126, the contents of each of which are hereby incorporated by reference.
Other types of stents are disclosed in the following patents:
U.S. Pat. No. 5,035,706 (Gianturco et al.), PA1 U.S. Pat. No. 5,037,392 (Hillstead), PA1 U.S. Pat. No. 5,147,385 (Beck et al.), PA1 U.S. Pat. No. 5,282,824 (Gianturco), PA1 Canadian patent 1,239,755 (Wallsten), and PA1 Canadian patent 1,245,527 (Gianturco et al.), PA1 " . . . no attempt should be made following placement of a PALMAZ-SCHATZ stent to access the side branch with a guide wire or a balloon, as such attempts may result in additional damage to the target vessel or the stent. Attempts to treat obstructed side branches within stented segments can result in balloon entrapment, necessitating emergency bypass surgery." PA1 1. Interventional Cardiovascular Medicine: Principles and Practice (1994); Publisher: Churchill Livingstone Inc.; pages 221-223 (Ohman et al.), 487-488 (Labinaz et al.), 667-668 (Bashore et al.) and 897 (Bailey et al.), including references cited therein; PA1 2. Gianturco-Roubin Flex-Stent.TM. Coronary Stent: Physician's Guide; page 2, Paragraph 3 under WARNINGS; PA1 3. Circulation, Vol. 83, No. 1, January 1991 (Schatz et al.); entitled "Clinical Experience With the Palmaz-Schatz Coronary Stent"; pages 148-161 at page 149; and PA1 4. American Heart Journal, Vol. 127, No. 2, February 1994 (Eeckhout et al.); entitled "Complications and follow-up after intracoronary stenting: Critical analysis of a 6-year single-center experience"; pages 262-272 at page 263, PA1 1. The stent is controllably expandable; PA1 2. The stent is flexible and thus, can be deliver via and/or implanted in curved body passageways; and PA1 3. Access to side branches is maintained, unlike the Palmaz-Schatz stent described hereinabove.
the contents of each of which are hereby incorporated by reference.
All of the stents described in the above-identified patents share the common design of being mono-tubular and thus, are best suited to be delivered and implanted in-line in the body passageway. These known stents are inappropriate for use in a bifurcated body passageway (e.g. a body passageway comprising a parent passageway that splits into a pair of passageways). Further, these stents are inappropriate for use in a body passageway having side branches since: (i) accurate placement of the stent substantially increases the risk to the patient, (ii) the risk of passageway closure in the side branches is increased, and (iii) the side branches will be substantially inaccessible.
Indeed the Physician Guide published in support of the Palmaz-Schatz stent states on page 32 (the contents of which are hereby incorporated by reference):
Thus, when installed, the Palmaz-Schatz stent admittedly shields side branches emanating from the target area of the body passageway effectively permanently. This can be problematic since the only way to treat blockage or other problems associated with the side branches is to perform the type of surgery which installation of the stent was intended to avoid.
This contraindication for conventional mono-tubular stents is corroborated by a number of investigators. See, for example, the following:
the contents of each of which are hereby incorporated by reference.
Further, some investigators have attempted to install individual stents in each branch of the bifurcated body passageway. However, this approach is fraught with at least two significant problems. First, implantation of three individual stents, together with the expansive forces generated upon implantation results in subjecting the central walls of the bifurcated body passageway to undue stress which may lead to post-procedural complications. Second, since the central walls of the bifurcated body passageway are not supported by the individual stents, this area of the passageway is left substantially unprotected and susceptible to blockage.
One particular problem area with bifurcated body passageways is the occurrence of bifurcation lesions within the coronary circulation. Generally, these legions may be classified as follows:
______________________________________ Type Characteristic ______________________________________ A Prebranch stenosis not involving the ostium of the side branch; B Postbranch stenosis of the parent vessel not involving the origin of the side branch; C Stenosis encompassing the side branch but not involving the ostium; D Stenosis involving the parent vessel and ostium of the side branch; E Stenosis involving the ostium of the side branch only; and F Stenosis discretely involving the parent vessel and ostium of the side branch. ______________________________________
See Atlas of Interventional Cardiology (Popma et al.), 1994, pages 77-79, the contents of which are hereby incorporated by reference. The presence of bifurcation lesions is predictive of increased procedural complications including acute vessel closure.
Detailed classification of other bifurcated body passageways is relatively undeveloped given the lack of non-surgical treatment approaches.
Indeed, to the knowledge of the Applicant's, heretofore, a proven expandable bifurcated stent has been unavailable.
It would be desirable to have an expandable bifurcated stent since this would be useful in treating aneurysms, blockages and other ailments. It would also be desirable if such a stent was relatively easy to install.